## Search

Now showing items 1-10 of 301

#### Studies of DC biasing of internal ring on plasma rotation and transport in a toroidal geometry

(Conference object; Konferansebidrag, 2004-10)

We report results from experiments performed to study how a DC bias with respect to
the plasma potential is affecting the plasma states in the toroidal geometry of the
Blaamann device in Tromso. In the experiments discussed here, a ring with smaller
diameter than the limiter was centered inside the bulk of the plasma and its bias varied
with respect to the plasma potential.
In the electron ...

#### On a class of linearizable planar geodesic webs

(Working paper; Arbeidsnotat, 2008-12-13)

We present a complete description of a class of linearizable planar
geodesic webs which contain a parallelizable 3-subweb.

#### Two models of population genetics

(Master thesis; Mastergradsoppgave, 2008-06-02)

The production of proteins in a cell is a regulated process. This means that the cell will only produce a type of protein when that type is needed. A fundamental step where this regulation occurs is at gene transcription. It is observed that transcription is regulated differently for different genes, and the question is therefore asked: why has evolution come up with different modes of transcriptional ...

#### Unsupervised segmentation of skin lesions

(Master thesis; Mastergradsoppgave, 2008-11-15)

During the last decades, the incidence rate of cutaneous malignant melanoma, a type of skin cancer developing from melanocytic skin lesions, has risen to alarmingly high levels. As there is no effective treatment for advanced melanoma, recognizing the lesion at an early stage is crucial for successful treatment. A trained expert dermatologist has an accuracy of around 75 % when diagnosing melanoma, ...

#### Dynamics and entropy in the Zhang model of Self-Organized Criticality

(Working paper; Arbeidsnotat, 2005-09-12)

We give a detailed study of dynamical properties of the Zhang model,
including evaluation of topological entropy and estimates for the Lyapunov
exponents and the dimension of the attractor. In the thermodynamic
limit the entropy goes to zero and the Lyapunov spectrum collapses.1

#### Entropy via multiplicity

(Working paper; Arbeidsnotat, 2005-09-30)

The topological entropy of piecewise affine maps is studied. It is shown
that singularities may contribute to the entropy only if there is angular expansion
and we bound the entropy via the expansion rates of the map. As
a corollary we deduce that non-expanding conformal piecewise affine maps
have zero topological entropy. We estimate the entropy of piecewise affine
skew-products. Examples of ...

#### A piece-wise affine contracting map with positive entropy

(Working paper; Arbeidsnotat, 2005-04-10)

We construct the simplest chaotic system with a two-point attractor.

#### Efficient intra-node Communication for Chip Multiprocessors

(Master thesis; Mastergradsoppgave, 2008-10-15)

The microprocessor industry has reached limitations of sequential processing power due to power-efficiency and heat problems. With the integrated-circuit technology moving forward, chip-multithreading has become the trend, increasing parallel processing power. The shift of focus has resulted in the vast majority of supercomputers having chip-multiprocessors.
While the high performance computing ...

#### A quadratic reciprocity law for elliptic curves

(Journal article; Tidsskriftartikkel; Peer reviewed, 2008)

If E is an elliptic curve, then the Galois group of the extension generated by the n-torsion points acts on these points. We prove a quadratic reciprocity law involving this group action. This law is an extension of the usual quadratic reciprocity law.

#### The pulsation modes of the pre-white dwarf PG 1159-035

(Journal article; Tidsskriftartikkel; Peer reviewed, 2008)

Context. PG 1159-035, a pre-white dwarf with Teff ≃ 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and
the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich
frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to ...